In recent years, minute machines, termed micromachines, have been proposed which are several millimeters or smaller in size, and extensive research is under way to develop such machines for actual use.
The drive systems already known for use with such micromachines include a wired system having a cable for feeding therethrough energy (electric power) and control signals from outside to a machine unit having an actuator as shown in FIG. 15A, and a wireless system for wirelessly feeding only control signals from outside to a machine unit which is internally provided with a battery or like energy source as seen in FIG. 15B.
In the case of the wired system, the energy source is provided outside the machine unit, so that the system has the advantages that the unit itself can be made smaller and that the micromachine can be designed with greater freedom since the amount of drive energy is not limited. However, the cable indispensable for the supply of energy imposes limitations on the operation range of the machine unit and on the movement thereof.
In the case of the wireless system, the machine unit is movable without limitations, whereas the need to mount the energy source on the machine unit for driving the unit increases the size and weight of the entire micromachine to impair the contemplated function of the micromachine.
An electrostatic motor has been proposed as a power generating mechanism for micromachines having the wired system. This motor comprises a rotor and a stator which are prepared from silicon or like semiconductor by photolithographic techniques. The rotor is rotatable by an electrostatic force acting between the rotor and the stator (see Journal of Japan Robot Society, Vol. 8, No. 4, August 1990, pp. 63-68).
However, the electrostatic motor has the problem of necessitating a complex peripheral circuit since the polarity of voltage to be applied to the blades of the rotor is alternately changed to positive and negative to realize continuous rotation.
Furthermore, the electrostatic force in the electrostatic motor is dependent on a point-to-point Coulomb's force generated by a charge at the outer end of the rotor blade and a charge at the outer end of the stator blade. This necessitates use of a high voltage of at least 100 V to obtain a great drive force. The voltage to be applied is high relative to the small size of the electrostatic motor which is about 200 micrometers in the diameter of the rotor and 2 to 3 micrometers in the distance between the rotor and the stator. Special consideration must therefore be given to space apart the rotor and the stator, and the adjacent blades of the stator against pressure.
Another problem is also encountered in that the peripheral circuit needs to be large-sized for controlling the high voltage of at least 100 V to be applied.